Added link to nominatim results in searching results

Fixes #3205. Added caching of nominatim URL query parameters in sources global variable (as parameters parameter) in GeocoderController#search for both direct and reverse geocoding. In app/views/geocoder/search.html.erb added displaying cached URL as forwarding link when clicked on "OpenStreetMap Nominatim" label. Updated GeocoderControllerTest to check only name (latlng, osm_nominatim, osm_nominatim_reverse) parameter of new sources variable.